Vibratory gyroscopes can measure rotation rate by sensing the motion of a moving proof mass. A Coriolis component of the motion of the moving proof mass is caused by a Coriolis force. The Coriolis force exists only when the gyroscope experiences an external rotation and is due to the Coriolis effect. The Coriolis force can be defined in vector notation by Equation 1, where i, j, and k represent the first, second, and third axes, respectively.
                                                        F              C                        →                                J            ^                          =                              -            2                    ⁢                      m            ⁡                          [                                                                    Ω                    →                                                        k                    ^                                                  ×                                                      v                    →                                                        ι                    ^                                                              ]                                                          (        1        )            
The Coriolis component is proportional to drive velocity as shown in Equations 2 and 3, where SF represents a constant scale factor that includes the mass of the proof mass as well as other constants related to the governing physics, electronics parameters, and the chosen sensor method employed to convert proof mass displacements to an output signal.
                                                    S            OUT            C                                    ∝                                                      F              →                        C                                    ∝                              -            2                    ⁢                                          ⁢          m          ⁢                                                Ω              →                                            ⁢                                                v              →                                                                      (        2        )                                                                Ω            →                                    =                  SF          ⁢                                                                  s                OUT                C                                                                                                v                →                                                                                      (        3        )            
Thus, if the drive velocity varies, the measurement of the rotation rate will also vary by a proportional amount. Systems and methods which do not take drift in drive velocity into account will be susceptible to reduced accuracy. These variations in drive velocity can be caused by degradation of springs, fluctuations in temperature, variations in device pressure, change in performance of closed-loop-drive analog electronics, changes in resonant frequency, changes in oscillator drive amplitude, applied inertial accelerations normal to the drive direction, changes in electronic loop gain, and acoustic signals applied to normal to the drive axis.